Arndale: Enable preboot support

We need to run 'usb start' as preboot command so that ethernet comes up
during u-boot prompt.

Signed-off-by: Tushar Behera <tushar.b@samsung.com>
Signed-off-by: Minkyu Kang <mk7.kang@samsung.com>
diff --git a/include/configs/arndale.h b/include/configs/arndale.h
index 30ecd45..370db82 100644
--- a/include/configs/arndale.h
+++ b/include/configs/arndale.h
@@ -229,6 +229,8 @@
 
 #define CONFIG_DEFAULT_DEVICE_TREE	exynos5250-arndale
 
+#define CONFIG_PREBOOT
+
 /* Ethernet Controllor Driver */
 #ifdef CONFIG_CMD_NET
 #define CONFIG_SMC911X